Figure 2.

Binding of soluble gp120 to cellular CD4 orCXCR4. Receptor binding efficiencies of gp120s were determined using a cell surface-binding assay in which bound protein was detected by Western blot analysis as described in Materials and Methods. Binding to CXCR4 was performed in the presence of sCD4 to expose the coreceptor binding site. HIV-1_IIIB and HIV-2_SBL gp120 exhibited relatively high CD4 binding efficiencies but weak CXCR4 binding. HIV-2_ROD gp120 exhibited relatively weak binding to CD4 and relatively high binding to CXCR4. Numbers indicate mean band intensity following subtraction of background pcDNA3 lane intensity.